1. Field of the Invention
The present invention relates to the configuration of an electro-optical display device, such as a projector using a liquid crystal panel and specifically to effective utilization of light in an optical system.
2. Description of the Related Art
In the field of electro-optical display devices, such as projectors using liquid crystal panels, there are techniques for effectively utilizing the light emitted from a light source.
One of those techniques is use of polarizing beam splitters (hereinafter referred to as PBSs). In conventional liquid crystal panels, polarizing plates are provided on the light incidence side and the light transmission side, respectively. The incidence-side polarizing plate transmits only a part of light incident on the liquid crystal panel which has a certain vibration plane and the other part of the incident light is not used. Therefore, the brightness of the liquid crystal panel depends on the transmittance of the incidence-side polarizing plate. The technique using PBSs intends to utilize the part of incident light that would otherwise be cut by the incidence-side polarizing plate. This technique will be outlined below with reference to FIGS. 2A and 2B.
As shown in FIG. 2B, light (including P waves and S waves) that has been emitted from a light source 204 is transmitted through a first lens array 205 and a second lens array 206 and enters a PBS array 207. The PBS array 207 is an array of a plurality of PBS units each comprising two PBSs and one half-wave plate.
FIG. 2A is an enlarged view of the PBS unit. Light coming from the second lens array 206 enters the first PBS and is thereby separated into P waves and S waves. The P waves reach a liquid crystal panel 209 as they are via an optical system 208 such as lenses. On the other hand, the S waves are reflected by the first PBS and enter the second PBS. The S waves are again reflected by the second PBS and then converted by the half-wave plate into P waves, which reach the liquid crystal panel 209 via the optical system 208.
As described above, this technique enables effective utilization of light by utilizing almost all of incident light as extracted P waves through repeated transmission and reflection by the PBSs. The PBS array 207 consists of a number of PBS units each measuring several centimeters. Each PBS unit provides lights that are to be incident on tens of pixels.
To realize color display by using this technique, a three-panel configuration using three dichroic mirrors and three liquid crystal panels or a single-panel configuration using color filters and a single liquid crystal panel is employed.
However, in the three-panel configuration, the PBS array is provided immediately downstream of the light source and light that is outputted from the PBS array is applied to the liquid crystal panels via the dichroic mirrors. Because a complex optical system exists between the PBS array and the liquid crystal panels, phase deviations again occur in the optical paths between the PBS array and the liquid crystal panels. As a result, the quantity of light that can be used actually is reduced and, it cannot make good use of the PBS array. In addition, because of the use of three liquid crystal panels, the three-panel configuration has a disadvantage of a high manufacturing cost.
In the conventional single-panel configuration using color filters, since light beams of respective colors are obtained by using color filters for the respective pixels, theoretically the light quantity is reduced to one third (⅓) in a case where three color filters of, for example, red, green, and blue are used. Actually, because of an additional factor of the transmittance of the color filters, the light quantity obtained is about (⅓)×0.7 of the original quantity.
Another technique for effective utilization of light is a singlepanel configuration not using color filters. This technique will be described below briefly with reference to FIGS. 3A and 3B.
As shown in FIG. 3A, light emitted from a white light source 301 is separated into a blue beam (B), a red beam (R), and a green beam (G) by three dichroic mirrors 302-304. The separated beams reach a liquid crystal panel 306 via a microlens array 305.
The separated beams enter apertures 310 of pixels corresponding to the respective beams as shown in FIG. 3B, enabling effective utilization of light. Further, since R, G, and B beams are generated from white light by the dichroic mirrors without using color filters, there is almost no loss of light.
As shown in FIG. 3A, light that has passed through the liquid crystal panel 306 reaches a screen 310 via a field lens 308 and a projection lens 309.
If the technique using PBSs is applied to the single-panel configuration not using color filters, the following problem occurs.
In the single-panel configuration not using color filters, beams of the respective colors are distributed to the corresponding pixels by the dichroic mirrors and the microlens array. However, in the technique using PBSs, each PBS unit can only produce light that enters tens of pixels. Therefore, to realize color display by combining the two techniques, the PBS array needs to be disposed between the white light source and the three dichroic mirrors.
In this configuration, a complex optical system exists in the optical path between the PBS array and the liquid crystal panel. Therefore, as pointed out above, phase deviations occur in the optical path between the PBS array and the liquid crystal panel, reducing the quantity of light that can be used actually. That is, there is a problem that the merit of the use of the PBS array cannot be exploited effectively.